Hey Rick, that is something I have also been wondering also. I cut a bunch of cane last fall and when I started sorting them I found some of the nock ends are too small for what I like. I have thought about drilling a hole in a slab of wood then cutting the side out to make a gauge. Then slide the gauge over the shaft until it hits the right diameter and cut it off there. That would be the nock end and hopefully all the point ends will be close to the same size when finished.
The river cane I cut will usually have a little bit of a flat spot running with the node, so I'll have to watch for that.
It may also be possible to find cane shafts that shoot well from a particular bow, then make a gauge for the nock end and cut shafts based on that nock size (speculation only at this point).
I have not noticed cane shrinking after cutting and drying, but I have never actually measured it "before and after".